The present invention relates to a method and a device for adjusting the braking and/or driving effect at the wheels of a motor vehicle.
A plurality of systems for anti-lock braking control, for traction control, and/or for vehicle stability in motor vehicles are known from the related art. These systems generally start from at least the wheel rotational speeds or the wheel speeds of the vehicle wheels. However, before the wheel speeds are used for regulation, they are generally corrected by a so-called tire tolerance adjustment. Such a regulating system for a motor vehicle is described in German Published Patent Application No. 42 30 295, for example, in which errors in the wheel speeds created by tolerances between the tires are equalized. Such tolerances are due to different wheel diameters, for example. For example, a low-pass filtering in conjunction with a tire tolerance adjustment is described in German Published Patent Application No. 42 30 295.
Furthermore, a slip regulation system is known, for example, from European Published Patent Application No. 0 510 466, where the wheel rotational speeds are used for slip formation. To equalize the tire tolerances, the wheel speeds are corrected. When determining the appropriate correction factors, possibly existing cornering of the vehicle must be taken into consideration.
The variations for adjusting tire tolerances known from the related art generally require relatively long time intervals. If the braking regulation and/or driving regulation is acted upon shortly after the vehicle is started, a slow tire tolerance adjustment can potentially result in unfavorable conditions.
If there is tire damage on a motor vehicle, often only a temporary spare wheel or spare wheel is provided. In contrast to standard wheels, this temporary spare wheel or spare wheel has a significantly smaller diameter which is to be taken into consideration by a tire tolerance adjustment. A detection of such temporary spare wheels or spare wheels is known from European Published Patent Application No. 0 449 845, for example.
As mentioned, the present invention relates to a method and a device for adjusting the braking effect and/or driving effect at the wheels of a motor vehicle. Assigned to the wheels are sensors that emit speed signals representing the rotary motions of the wheels. These speed signals are corrected via a correction, i.e., the tire tolerance adjustment. The braking and/or driving effect is/are adjusted at least as a function of corrected sensor speed signals.
According to the present invention, the correction, i.e., the tire tolerance adjustment, has at least two different modes of operation. Furthermore, it is determined whether a mounted spare wheel or temporary spare wheel having a smaller diameter than the remaining wheels is present. One of the operating modes is then selected in accordance with the present invention, as a function of the determined existence of a spare wheel.
According to the present invention, a selection module is connected in series with and upstream from the actual tire tolerance adjustment, the selection module selecting a specific operating mode in response to a temporary spare wheel being present. This certain operating mode of the tire tolerance adjustment advantageously enables a particularly quick tire tolerance adjustment. The actual, slow tire tolerance adjustment, which is, however, generally more precise, follows the first, quick tire tolerance adjustment. As a result of this adjustment algorithm, the rotational speed of a temporary spare wheel or spare wheel is very quickly adjusted to the other wheel speeds. As a result of the present invention, the temporary spare wheel adjustment is carried out in such a manner that the complete functionality of an anti-lock control system, traction control system, and/or vehicle stability system or of an electronic braking force distribution system is already present when braking for the first time. Thus, no additional measures are necessary.
In an advantageous embodiment of the present invention, it is provided that the correction, i.e., the tire tolerance adjustment, is carried out more quickly in a first operating mode having a smaller filtering time constant than in a second operating mode having a larger filtering time constant.
A further embodiment of the present invention start from the assumption that the standard, slow tire tolerance adjustment is carried out as a function of the output torque of the vehicle engine. This can be inferred, for example, from the document German Published Patent Application No. 42 30 295 mentioned at the outset. Thus, for the standard, i.e., slow, tire tolerance adjustment, a certain condition is given for the engine torque in order for the tire tolerance adjustment to be carried out. For example, the drive torque or the drag torque acting on the wheels is sufficiently low. However, this condition slows the tire tolerance adjustment in cases in which the engine torque does not satisfy this condition. According to this embodiment of the present invention, it is provided that the correction is carried out in a first, quick operation mode of the tire tolerance adjustment, independently of the engine torque.
It is further known to attach the tire tolerance adjustment to the condition that no cornering exists. In an additional embodiment of the present invention, it is provided that it be determined whether the vehicle is traveling on a curve. According to this embodiment, the tire tolerance adjustment is performed in the first, quick operating mode, independently of determined cornering.
In a further embodiment of the present invention, it is provided that, in the first, quick operating mode, the tire tolerance adjustment is performed at lower forward speeds of the vehicle than in a second, slower operating mode.
However, the determination of whether there is a mounted temporary spare wheel or spare wheel is advantageously only begun when a predefinable speed threshold value for the vehicle""s forward speed is exceeded.
In a further advantageous embodiment of the present invention, it is provided that the determination of whether there is a mounted temporary spare wheel or spare wheel occurs in such a manner that
the wheel having the highest rotational speed is determined from the speed signals;
a check is performed to determine whether the rotational speed of the wheel having the highest rotational speed deviates in a predefinable manner from the rotational speed having the speed of at least one other wheel, in particular of the wheel mounted on the same vehicle axle;
it is determined from the differences of the rotational speeds of the wheels on the axle on which the wheel having the highest rotational speed is not mounted whether cornering exists; and
the wheel having the highest rotational speed is determined as the temporary spare wheel or spare wheel provided that the rotational speed of this wheel deviates in a predefinable manner and especially for a predefinable period of time from the rotational speed of at least one other wheel, and there is no cornering.
In a further embodiment of the present invention, it is provided that the mode selected when a temporary spare wheel or spare wheel is present is terminated as a function of the result of a comparison of the corrected output signal of the temporary spare wheel or the spare wheel to an output signal of at least one sensor at another wheel. This is because the quick and tolerant tire tolerance adjustment is only intended to enable a first, quick adaptation of the temporary spare wheel to the reference wheel. The standard tire tolerance adjustment including its release conditions is to subsequently apply again. The quick and tolerant tire tolerance adjustment is, therefore, ended when the rotational speed of the temporary spare wheel or spare wheel deviates less than 1.5%, for example, from the other wheel rotational speeds.